.topSer {
    background-color: white;
}
.topSer a {
    color: #254375;
}
.allBack {
    width: 100%;
    background-image: url(https://zhang0228.oss-cn-wulanchabu.aliyuncs.com/beijing.jpg);
    background-repeat: no-repeat;
    background-size: 100% 5757px;
}
.main {
    position: relative;
    width: 3840px;
    height: 2455px;
    margin: auto;
}
.main a {
    color: #254375;
}
.huan {
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
    left: 400px;
    width: 1300px;
    height: 377px;
    background-color: white;
    line-height: 377px;
    text-align: center;
    font-size: 125px;
    border-radius: 50px;
}
.jie{
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
    right: 400px;
    width: 1300px;
    height: 377px;
    background-color: white;
    line-height: 377px;
    text-align: center;
    font-size: 125px;
    border-radius: 50px;
}